Curable base-resistant fluoroelastomers

ABSTRACT

A base resistant, substantially amorphous fluoroelastomer comprising (1) 10-40 mole percent ethylene units, (2) 32-60 mole percent tetrafluoroethylene units, (3) 20-40 mole percent perfluoro ether units selected from the group consisting of perfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenyl ethers), and (4) 0.1 to 15 mole percent of a cure site monomer selected from the group consisting of i) 3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene. Such fluoroelastomers may be vulcanized with polyhydroxy curatives. The resulting vulcanized fluoroelastomer compositions are resistant to attack by amines, strong bases and hydrogen sulfide and possess a combination of good low temperature and high temperature properties and they are resistant to oil swell.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/290,905 filed May 15, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to polyhydroxy curable fluoroelastomerscomprising copolymerized units of 1) ethylene, 2) a perfluoro ether suchas a perfluoro(alkyl vinyl ether) or a perfluoro(alkyl or alkoxy alkenylether), 3) tetrafluoroethylene, and 4) a cure site monomer selected fromthe group consisting of i) 3,3,3-trifluoropropene-1, ii)trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv)1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene.

BACKGROUND OF THE INVENTION

[0003] Base resistant specialty fluoroelastomers made from copolymers ofethylene (E), a perfluoro(alkyl vinyl ether) (PAVE), tetrafluoroethylene(TFE) and a cure site monomer are known in the art (U.S. Pat. No.4,694,045). In addition to being resistant to attack by strong bases,these fluoroelastomers have good sealing properties at both low and hightemperatures and exhibit low swell in oil.

[0004] In order to fully develop physical properties such as tensilestrength, elongation, and compression set, elastomers must be cured,i.e. crosslinked. In the case of fluoroelastomers, this is generallyaccomplished by mixing uncured polymer (i.e. fluoroelastomer gum) with apolyfunctional curing agent and heating the resultant mixture, therebypromoting chemical reaction of the curing agent with active sites alongthe polymer backbone or side chains. Interchain linkages produced as aresult of these chemical reactions cause formation of a crosslinkedpolymer composition having a three-dimensional network structure.Commonly used curing agents for fluoroelastomers include difunctionalnucleophilic reactants, such as polyhydroxy compounds or diamines.Alternatively, peroxidic curing systems containing organic peroxides andunsaturated coagents, such as polyfunctional isocyanurates, may beemployed.

[0005] U.S. Pat. No. 4,694,045 discloses several cure site monomerswhich may be incorporated into E/PAVE/TFE specialty fluoroelastomers.These include brominated or iodinated alpha-olefins, and varioushalogenated vinyl ethers. Such fluoroelastomers may be cured withperoxides or tin compounds, but not polyhydroxy curatives. However, inmany end use applications, it would be beneficial to be able to cureE/PAVE/TFE fluoroelastomers with polyhydroxy compounds because of theimproved mold release properties and superior resistance to compressionset (i.e. lower compression set) that is imparted by this type ofcrosslinking system.

[0006] Thus, it would be particularly desirable to have an improvedspecialty E/PAVE/TFE fluoroelastomer that is resistant to alkalinefluids and oil swell and which readily crosslinks with polyhydroxy curesystems to form cured articles having good tensile properties andcompression set resistance.

SUMMARY OF THE INVENTION

[0007] It has been surprisingly found that the introduction of a curesite monomer selected from the group consisting of i)3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii)1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, andv) 2,3,3,3-tetrafluoropropene into ethylene/perfluoroether/tetrafluoroethylene copolymers improves the polyhydroxy curing ofthese specialty fluoroelastomers without significantly diminishing theresistance of these fluoroelastomers to alkaline fluids or oil andwithout significantly altering the low and high temperature sealingcapabilities of these fluoroelastomers. The resulting curedfluoroelastomer articles have excellent compression set resistance andtensile properties.

[0008] Accordingly, an aspect of the present invention is a specialtyfluoroelastomer comprising copolymerized units of 10 to 40 mole percentethylene; 20 to 40 mole percent of a perfluoro ether selected from thegroup consisting of perfluoro(alkyl vinyl ethers), perfluoro(alkylalkenyl ethers) and perfluoro(alkoxy alkenyl ethers); 32-60 mole percenttetrafluoroethylene; and 0.1 to 15 mole percent of a cure site monomerselected from the group consisting of i) 3,3,3-trifluoropropene-1, ii)trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv)1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene.

[0009] Another aspect of this invention is a curable fluoroelastomercomposition comprising

[0010] A) a specialty fluoroelastomer comprising copolymerized units of10 to 40 mole percent ethylene; 20 to 40 mole percent of a perfluoroether selected from the group consisting of perfluoro(alkyl vinylethers), perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenylethers); 32-60 mole percent tetrafluoroethylene; and 0.1 to 15 molepercent of a cure site monomer selected from the group consisting of i)3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii)1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, andv) 2,3,3,3-tetrafluoropropene;

[0011] B) 0.1 to 20 parts by weight per 100 parts fluoroelastomer of apolyhydroxy curing agent;

[0012] C) 1 to 30 parts by weight per 100 parts fluoroelastomer of anacid acceptor; and

[0013] D) 0.1 to 20 parts per 100 parts fluoroelastomer of avulcanization accelerator.

[0014] The polyhydroxy curing agent and vulcanization accelerator may bepresent as separate components or as the salt of the curing agent andaccelerator.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Fluoroelastomers of this invention comprise copolymerized unitsof 1) ethylene (E), 2) a perfluoro ether selected from the groupconsisting of perfluoro(alkyl vinyl ethers) (PAVE), perfluoro(alkylalkenyl ethers) and perfluoro(alkoxy alkenyl ethers), 3)tetrafluoroethylene (TFE), and 4) a cure site monomer selected from thegroup consisting of i) 3,3,3-trifluoropropene-1 (TFP), ii)trifluoroethylene (TrFE), iii) 1,2,3,3,3-pentafluoropropylene (1-HPFP),iv) 1,1,3,3,3-pentafluoropropylene (2-HPFP), and v)2,3,3,3-tetrafluoropropene.

[0016] Minor amounts (i.e. less than about 20 mole percent total) ofother copolymerizable monomers may also be present in thefluoroelastomers of this invention. Examples of such monomers include,but are not limited to chlorotrifluoroethylene; vinyl fluoride;propylene; isobutene; and bromine- or iodine-containing cure sitemonomers such as CF₂═CFOCF₂CF₂CF₂OCF₂CF₂Br;1-bromo-2,2-difluoroethylene; bromotrifluoroethylene;4-bromo-3,3,4,4-tetrafluorobutene-1,4-bromo-1,1,2-trifluorobutene-1;2-bromoperfluoro(ethyl vinyl) ether; 3-bromoperfluoro(propyl vinyl)ether; and 4-iodo-3,3,4,4-tetrafluorobutene-1. Alternatively, bromine oriodine cure sites may optionally be introduced onto the fluoroelastomerpolymer chain ends by use of iodinated or brominated chain transferagents such as methylene iodide or 1,4-diiodoperfluoro-butane duringpolymerization. The presence of brominated or iodinated groups permitsthe fluoroelastomers of this invention to be cured by organic peroxidesin addition to polyhydroxy curatives.

[0017] Generally the fluoroelastomers of this invention contain between10 to 40 (preferably between 20 to 40) mole percent copolymerized unitsof ethylene, based on the total moles of copolymerized monomers. Lessethylene adversely effects the low temperature sealing performance ofthe fluoroelastomers, while more ethylene adversely effects the baseresistance and oil swell resistance properties of the fluoroelastomers.

[0018] The fluoroelastomers of this invention typically contain between20 to 40 (preferably between 20 to 30) mole percent copolymerized unitsof a perfluoro ether selected from the group consisting ofperfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenyl ethers) andperfluoro(alkoxy alkenyl ethers), based on the total moles ofcopolymerized monomers. Less perfluoro ether will negatively impact thelow temperature sealing performance of the fluoroelastomers of theinvention, while more perfluoro ether causes the polymer to be moreexpensive to produce.

[0019] Perfluoro(alkyl vinyl ethers) suitable for use as monomersinclude those of the formula

CF₂═CFO(R_(f′)O)_(n)(R_(f″)O)_(m)R_(f)(I)

[0020] where R_(f′) and R_(f″) are different linear or branchedperfluoroalkylene groups of 2-6 carbon atoms, m and n are independently0-10, and R_(f) is a perfluoroalkyl group of 1-6 carbon atoms.

[0021] A preferred class of perfluoro(alkyl vinyl ethers) includescompositions of the formula

CF₂═CFO(CF₂CFXO)_(n)R_(f)  (II)

[0022] where X is F or CF₃, n is 0-5, and R_(f) is a perfluoroalkylgroup of 1-6 carbon atoms.

[0023] A most preferred class of perfluoro(alkyl vinyl ethers) includesthose ethers wherein n is 0 or 1 and R_(f) contains 1-3 carbon atoms.Examples of such perfluorinated ethers include perfluoro(methyl vinylether) (PMVE) and perfluoro(propyl vinyl ether) (PPVE). Other usefulmonomers include compounds of the formula

CF ₂═CFO[(CF₂)_(m)CF₂CFZO]_(n)R_(f)  (III)

[0024] where R_(f) is a perfluoroalkyl group having 1-6 carbon atoms, m=0 or 1, n=0-5, and Z=F or CF₃.

[0025] Preferred members of this class are those in which R_(f) is C₃F₇,m=0, and n=1.

[0026] Additional perfluoro(alkyl vinyl ether) monomers includecompounds of the formula

CF₂═CFO[(CF₂CF{CF₃}O)_(n)(CF₂CF₂CF₂O)_(m)(CF₂)_(p)]C_(x)F_(2x+1)  (IV)

[0027] where m and n independently=0-10, p=0-3, and x=1-5. Preferredmembers of this class include compounds where n=0-1, m=0-1, and x=1.

[0028] Additional examples of useful perfluoro(alkyl vinyl ethers)include

CF₂═CFOCF₂CF(CF₃)O(CF₂O)_(m)C_(n)F_(2n+1)  (V)

[0029] where n=1-5, m=1-3, and where, preferably, n=1.

[0030] Perfluoro(alkyl alkenyl ethers) suitable for use as monomersinclude those of the formula VI

R_(f)O(CF₂)_(n)CF═CF₂  (VI)

[0031] where R_(f) is a perfluorinated linear or branched aliphaticgroup containing 1-20, preferably 1-10, and most preferably 1-4 carbonatoms and n is an integer between 1 and 4. Specific examples include,but are not limited to perfluoro(propoxyallyl ether) andperfluoro(propoxybutenyl ether).

[0032] Perfluoro(alkoxy alkenyl ethers) differ from perfluoro(alkylalkenyl ethers) in that R_(f) in formula VI contains at least one oxygenatom in the aliphatic chain. A specific example includes, but is notlimited to perfluoro(methoxyethoxyallyl ether).

[0033] Also contained in the fluoroelastomers of this invention isbetween 32-60 (preferably 40 to 50) mole percent copolymerized units oftetrafluoroethylene, based on the total moles of copolymerized monomers.Less TFE will adversely effect oil swell resistance whereas higherlevels of TFE may introduce crystallinity, thus negatively impactingelastomer properties such as elongation and compression set.

[0034] The fluoroelastomers of this invention also contain 0.1 to 15(preferably 2 to 10, most preferably 2-6) mole percent (based on thetotal moles of copolymerized monomers) of copolymerized units of a curesite monomer. The cure site monomer is selected from the groupconsisting of i) 3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii)1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, andv) 2,3,3,3-tetrafluoropropene.

[0035] It is believed that during the polyhydroxy curing process, somecopolymerized units of the cure site monomer, which are located adjacentto tetrafluoroethylene units in the fluoroelastomer polymer chain,dehydrofluorinate to form sites of unsaturation (i.e. C—C double bonds).These unsaturated sites are then available to react with polyhydroxycuratives to form crosslinks. Fluoroelastomers containing less than 0.1mole percent units of one of these cure site monomers do not form asufficient number of crosslinks to yield a cured product havingdesirable tensile properties for most end uses. Fluoroelastomerscontaining more than 15 mole percent of these cure site monomers are notdesirable because i) the polymerization rate is reduced and ii) the baseresistance property of the fluoroelastomer is reduced.

[0036] The fluoroelastomers of this invention are generally prepared byfree radical emulsion or suspension polymerization. Preferably, thepolymerizations are carried out in continuous, batch, or semi-batchemulsion processes well known in the art. The resulting fluoroelastomerlatexes are usually coagulated by addition of electrolytes. Theprecipitated polymer is washed with water and then dried, for example inan air oven, to produce a substantially dry fluoroelastomer gum.

[0037] In a semi-batch emulsion polymerization process, a gaseousmonomer mixture of a desired composition (initial monomer charge) isintroduced into a reactor which contains an aqueous solution. Generally,the pH of the aqueous solution is controlled to between 1 and 8(preferably 3-7), depending upon the type of fluoroelastomer being made.In addition, the initial aqueous solution may contain a nucleatingagent, such as a fluoroelastomer seed polymer prepared previously, inorder to promote fluoroelastomer latex particle formation and thus speedup the polymerization process.

[0038] The initial monomer charge contains a quantity of TFE, E,perfluoro ether and cure site monomer. The amount of monomer mixturecontained in the initial charge is set so as to result in a reactorpressure between 0.5 and 10 MPa.

[0039] The monomer mixture is dispersed in the aqueous medium and,optionally, a chain transfer agent may also be added at this point whilethe reaction mixture is agitated, typically by mechanical stirring.

[0040] The temperature of the semi-batch reaction mixture is maintainedin the range of 25° C.-130°C., preferably 50° C.-100° C. Polymerizationbegins when the initiator either thermally decomposes or reacts withreducing agent and the resulting radicals react with dispersed monomer.

[0041] Additional quantities of the gaseous major monomers and cure sitemonomer (incremental feed) are added at a controlled rate throughout thepolymerization in order to maintain a constant reactor pressure at acontrolled temperature. The polymerization pressure is controlled in therange of 0.5 to 10 MPa, preferably 1 to 6.2 MPa.

[0042] Polymerization times in the range of from 2 to 30 hours aretypically employed in this semi-batch polymerization process.

[0043] A suitable continuous emulsion polymerization process differsfrom the semi-batch process in the following manner. In the continuousprocess, gaseous monomers and solutions of other ingredients such aswater-soluble monomers, chain transfer agents, buffer, bases,polymerization initiator, surfactant, etc., are fed to the reactor inseparate streams at a constant rate. The temperature of the continuousprocess reaction mixture is maintained in the range of 25° C.-130° C.,preferably 80° C.-120° C.

[0044] Curable compositions of this invention contain thefluoroelastomer of this invention, a polyhydroxy curative, an acidacceptor and a vulcanization (or curing) accelerator. In the case offluoroelastomers which contain bromine or iodine atom cure sites, thecurable compositions of this invention may, optionally, also contain anorganic peroxide and a multifunctional curing coagent. Cured articlesresulting from the latter compositions contain crosslinks due to boththe polyhydroxy and peroxide curing systems and are sometimes referredto in the art as dual cured elastomers.

[0045] The curable compositions of the invention contain between 0.1 to20 parts by weight (preferably 1-3 parts) of polyhydroxy crosslinkingagent per 100 parts fluoroelastomer. Typical polyhydroxy cross-linkingagents include di-, tri-, and tetrahydroxybenzenes, naphthalenes, andanthracenes, and bisphenols of the formula

[0046] where A is a difunctional aliphatic, cycloaliphatic, or aromaticradical of 1-13 carbon atoms, or a thio, oxy, carbonyl, sulfinyl, orsulfonyl radical; A may optionally be substituted with at least onechlorine or fluorine atom; x is 0 or 1; n is 1 or 2; and any aromaticring of the polyhydroxylic compound may optionally be substituted withat least one chlorine or fluorine atom, an amino group, a —CHO group, ora carboxyl or acyl radical. Phenolate salts are also active crosslinkingagents, such as the dipotassium salt of bisphenol AF. Preferredpolyhydroxy compounds includehexafluoroisopropylidene-bis(4-hydroxy-benzene) (i.e. bisphenol AF);4,4′-isopropylidene diphenol (i.e. bisphenol A); 4,4′-dihydroxydiphenylsulfone; and diaminobisphenol AF. Referring to the bisphenol formulashown above, when A is alkylene, it can be for example methylene,ethylene, chloroethylene, fluoroethylene, difluoroethylene, propylidene,isopropylidene, tributylidene, heptachlorobutylidene,hepta-fluorobutylidene, pentylidene, hexylidene, and1,1-cyclohexylidene. When A is a cycloalkylene radical, it can be forexample 1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene, cyclopentylene,or 2-fluoro-1,4-cyclohexylene. Further, A can be an arylene radical suchas m-phenylene, p-phenylene, o-phenylene, methyl-phenylene,dimethylphenylene, 1,4-naphthylene, 3-fluoro-1,4-naphthylene, and2,6-naphthylene. Polyhydroxyphenols of the formula

[0047] where R is H or an alkyl group having 1-4 carbon atoms or an arylgroup containing 6-10 carbon atoms and R′ is an alkyl group containing1-4 carbon atoms also act as effective crosslinking agents. Examples ofsuch compounds include hydroquinone, catechol, resorcinol,2-methylresorcinol, 5-methyl-resorcinol, 2-methylhydroquinone,2,5-dimethylhydroquinone, 2-t-butyl-hydroquinone; and such compounds as1,5-dihydroxynaphthalene and 2,6-dihydroxynaphthalene.

[0048] Additional polyhydroxy curing agents include alkali metal saltsof bisphenol anions, quaternary ammonium salts of bisphenol anions,tertiary sulfonium salts of bisphenol anions and quaternary phosphoniumsalts of bisphenol anions. For example, the salts of bisphenol A andbisphenol AF. Specific examples include the disodium salt of bisphenolAF, the dipotassium salt of bisphenol AF, the monosodium monopotassiumsalt of bisphenol AF and the benzyltriphenylphosphonium salt ofbisphenol AF.

[0049] Quaternary ammonium and phosphonium salts of bisphenol anions andtheir preparation are discussed in U.S. Pat. Nos. 4,957,975 and5,648,429. Bisphenol AF salts (1:1 molar ratio) with quaternary ammoniumions of the formula R₁R₂R₃R₄N⁺, wherein R₁-R₄ are C₁-C₈ alkyl groups andat least three of R₁-R₄ are C₃ or C₄ alkyl groups are preferred.Specific examples of these preferred compositions include the 1:1 molarratio salts of tetrapropyl ammonium-, methyltributylammonium- andtetrabutylammonium bisphenol AF. Such salts may be made by a variety ofmethods. For instance a methanolic solution of bisphenol AF may be mixedwith a methanolic solution of a quaternary ammonium salt, the pH is thenraised with sodium methoxide, causing an inorganic sodium salt toprecipitate. Alternatively, a methanolic solution of bisphenol AF mayfirst be neutralized with a molar equivalent of base (such as sodiummethoxide). The quaternary ammonium salt is then added and an inorganicsalt precipitates. After filtration, the tetraalkylammonium/BPAF saltmay be isolated from solution by evaporation of the methanol. In anothermethod for preparing the curative/accelerator salt, a methanolicsolution of tetraalkylammonium hydroxide may be employed in place of thesolution of quaternary ammonium salt, thus eliminating the precipitationof an inorganic salt and the need for its removal prior to evaporationof the methanol.

[0050] In addition, derivatized polyhydroxy compounds, such as mono- ordiesters and trimethylsilyl ethers, are useful crosslinking agents.Examples of such compositions include diesters of phenols, such as thediacetate of bisphenol AF, the diacetate of sulfonyl diphenol, and thediacetate of hydroquinone.

[0051] The curable compositions of the invention also contain between 1to 30 parts by weight (preferably 1 to 15 parts) of an acid acceptor per100 parts fluoroelastomer. The acid acceptor is typically a strongorganic base such as Proton Sponge® (available from Aldrich) or anoxirane, or an inorganic base such as a metal oxide, metal hydroxide, ora mixture of 2 or more of the latter. Metal oxides or hydroxides whichare useful acid acceptors include calcium hydroxide, magnesium oxide,lead oxide, and calcium oxide. Calcium hydroxide and magnesium oxide arepreferred.

[0052] Vulcanization accelerators which may be used in the curablecompositions of the invention include tertiary sulfonium salts such as[(C₆H₅)₂S⁺(C₆H₁₃)][Cl]⁻, and [(C₆H₁₃)₂S(C₆H₅)]⁺[CH₃CO₂]⁻ and quaternaryammonium, phosphonium, arsonium, and stibonium salts of the formulaR₅R₆R₇R₈Y⁺X⁻, where Y is phosphorous, nitrogen, arsenic, or antimony;R₅, R₆, R₇, and R₈ are individually C₁-C₂₀ alkyl, aryl, aralkyl,alkenyl, alkoxy and the chlorine, fluorine, bromine, cyano, —OR, and—COOR substituted analogs thereof, with R being C₁-C₂₀ alkyl, aryl,aralkyl, alkenyl, and where X is halide, hydroxide, sulfate, sulfite,carbonate, pentachlorothiophenolate, tetrafluoroborate,hexafluorosilicate, hexafluorophosphate, dimethyl phosphate, and C₁-C₂₀alkyl, aryl, aralkyl, and alkenyl carboxylates and dicarboxylates.Particularly preferred are benzyltri-phenylphosphonium chloride,benzyltriphenylphosphonium bromide, tetrabutylammonium hydrogen sulfate,tetrabutylammonium hydroxide, tetrapropylammonium hydroxide,tetrabutylammonium bromide, tributylallylphosphonium chloride,tributyl-2-methoxypropylphosphonium chloride,1,8-diazabicyclo[5.4.0]undec-7-ene, and benzyldiphenyl(dimethylamino)phosphonium chloride. Other useful accelerators includemethyltrioctylammonium chloride, methyltributylammonium chloride,tetrapropylammonium chloride, benzyltrioctylphosphonium bromide,benzyltrioctylphosphonium chloride, methyltrioctylphosphonium acetate,tetraoctylphosphonium bromide, methyltriphenylarsoniumtetrafluoroborate, tetraphenylstibonium bromide, 4-chlorobenzyltriphenylphosphonium chloride, 8-benzyl-1,8-diazabicyclo(5.4.0)-7-undecenoniumchloride, diphenylmethyltriphenylphosphonium chloride,allyltriphenyl-phosphonium chloride, tetrabutylphosphonium bromide,m-trifluoromethyl-benzyltrioctylphosphonium chloride, and otherquaternary compounds disclosed in U.S. Pat. Nos. 5,591,804; 4,912,171;4,882,390; 4,259,463; 4,250,278 and 3,876,654. The amount of acceleratorused is between 0.1 and 20 parts by weight per hundred partsfluoroelastomer. Preferably, 0.5-3.0 parts accelerator per hundred partsfluoroelastomer is used.

[0053] Optionally, the curable compositions of the invention may containa second curing agent in the form of a combination of an organicperoxide and a multifunctional (i.e. polyunsaturated) coagent compound.Examples of organic peroxides which are particularly effective curingagents for fluoroelastomers include dialkyl peroxides or bis(dialkylperoxides) which decompose at a temperature above 50° C. In many casesone will prefer to use a di-t-butylperoxide having a tertiary carbonatom attached to a peroxy oxygen. Among the most useful are2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 and2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane. Other peroxides can beselected from such compounds as dicumyl peroxide, dibenzoyl peroxide,t-butyl perbenzoate, anddi[1,3-dimethyl-3-(t-butyl-peroxy)butyl]carbonate. Multifunctionalcoagents which cooperate with such peroxides to provide curing systemsinclude methacrylates, allyl compounds, divinyl compounds, andpolybutadienes. Specific examples of coagents include one or more of thefollowing compounds: triallyl cyanurate; triallyl isocyanurate;tris(diallylamine-s-triazine); triallyl phosphite; hexaallylphosphoramide, N,N-diallyl acrylamide; N,N,N′N′-tetraallylterephthalamide; N,N,N′,N′-tetraallyl malonamide; trivinyl isocyanurate;2,4,6-trivinylmethyltrisiloxane; andtri(5-norbornene-2-methylene)cyanurate. If a peroxide cure system ispresent in the compounds of the invention, the organic peroxide isgenerally at a level between 0.2 to 7 parts by weight (preferably 1 to 3parts) per 100 parts fluoroelastomer and the coagent is present at alevel of 0.1 to 10 (preferably 2 to 5) parts by weight per 100 partsfluoroelastomer.

[0054] The curable composition of the invention may contain otheradditives, commonly used in elastomer compounding and processing. Thelatter may be introduced into the composition before addition of thecurative, simultaneously with it, or following the addition. Typicaladditives include fillers, plasticizers, processing aids, antioxidants,pigments, and the like. The amount of such ingredients which is addedwill depend on the particular end use applications for which the curedcompositions are adapted. Fillers, such as carbon black, clays, bariumsulfate, calcium carbonate, magnesium silicate, and fluoropolymers aregenerally added in amounts of from 5-100 parts by weight per 100 partsfluoroelastomer. The amount of plasticizer used is generally from0.5-5.0 parts by weight per 100 parts fluoroelastomer. Typicalplasticizers include esters, such as dioctyl phthalate and dibutylsebacate. Processing aids are generally used in amounts of from 0.1-2.0parts by weight per 100 parts fluoroelastomer. Suitable processing aidsinclude octadecylamine, tetramethylene sulfone, p-chlorophenyl sulfone,and waxes, for example, carnauba wax, that aid in the processing of thecompositions.

[0055] The fluoroelastomer, polyhydroxy curative, acid acceptor,accelerator and any other ingredients are generally incorporated intothe curable compositions of the invention by means of an internal mixeror rubber mill. The resulting composition may then be shaped (e.g.molded or extruded) and cured. Curing typically takes place at about150°-200° C. for 1 to 60 minutes. Conventional rubber curing presses,molds, extruders, and the like provided with suitable heating and curingmeans can be used. Also, for maximum heat resistance and dimensionalstability, it is preferred to carry out a post curing operation whereinthe molded or extruded article is heated in an oven or the like for anadditional period of about 1-48 hours, typically at from about 180°-275°C., generally in an air atmosphere.

[0056] The polymers of the invention and curable compositions of theinvention result in cured fluoroelastomer articles which have unusuallygood base resistance, tensile properties and compression set resistance.Such articles find application as gaskets, seals and tubing,particularly in automotive end uses.

[0057] The invention is now illustrated by the following embodiments inwhich all parts are by weight unless otherwise indicated.

EXAMPLES

[0058] Test Methods

[0059] Physical properties of the compositions described in the exampleswere measured according to the following test procedures. Mooney ScorchASTM D1646 Oscillating Disc Rheometer (ODR) ASTM D2084 Moving DiscRheometer (MDR) ASTM D5289 Tensile Strength (T_(B)) ASTM D412 Modulus(M₁₀₀) ASTM D412 Elongation at Break (E_(B)) ASTM D412 Hardness ASTMD2240 Compression Set-B ASTM D395

Example 1

[0060] A polymer of the invention (Polymer 1) was prepared by acontinuous emulsion polymerization process, carried out at 110° C. in awell-stirred 4.0-liter stainless steel liquid full reaction vessel. Anaqueous solution, consisting of 2.7 g/hour (g/h) ammonium persulfate,22.2 g/h sodium phosphate dibasic heptahydrate, and 22.2 g/h of ammoniumperfluorooctanoate, was fed to the reactor at a rate of 2 L/hour. Thereactor was maintained at a liquid-full level at a pressure of 6.2 MPaby means of a backpressure control valve in the effluent line. After 30minutes, polymerization was initiated by introduction of a gaseousmonomer mixture consisting of 6.1 wt. % ethylene (E), 36.9 wt. %tetrafluoroethylene (TFE), 51.3 wt. % perfluoro(methyl vinyl ether)(PMVE) and 5.8 wt. % 1,1,3,3,3-pentafluoropropylene (2H-PFP) fed througha diaphragm compressor. After 2.0 hours, collection of effluentdispersion was begun and lasted for 6 hours. The effluent polymerdispersion, which had a pH of 4.4 and contained 26 wt. % solids, wasseparated from residual monomers in a degassing vessel at atmosphericpressure. The resulting fluoroelastomer latex was coagulated by additionof an aqueous calcium nitrate solution, filtered and then thefluoroelastomer was washed with deionized water. The wet crumb was driedin an air oven at approximately 50°-65° C. to a moisture content of lessthan 1 wt. %. About 4 kg of polymer was recovered at an overallconversion of 77.6%. The product, composed of 7.8 wt. % ethylene, 44.2wt. % TFE, 47.0 wt. % PMVE and 1.0 wt. % 2H-PFP units, was an amorphousfluoroelastomer having a glass transition temperature of −10° C., asdetermined by differential scanning calorimetry (heating mode, 10°C./minute, inflection point of transition). Mooney viscosity, ML-10(121° C.), was 50.

Example 2

[0061] A polymer of the invention (Polymer 2) was prepared by asemi-batch emulsion polymerization process, carried out at 80° C. in awell-stirred reaction vessel. A 33-liter, horizontally agitated reactorwas charged with 20 liters of deionized, deoxygenated water, 200 g ofammonium perfluorooctanoate and 100 g of sodium phosphate dibasicheptahydrate. The reactor was heated to 80° C. and then pressurized to2.07 MPa with a mixture of 14.5 wt. % TFE, 85.3 wt. % PMVE and 0.2 wt. %3,3,3-trifluoropropene-1 (TFP). A 35 ml sample of a 10 wt. % ammoniumpersulfate initiator aqueous solution was then added. A mixture of 7.7wt. % ethylene, 42.3 wt. % TFE, 47.0 wt. % PMVE and 3.0 wt. % TFP wassupplied to the reactor to maintain a pressure of 2.07 MPa throughoutthe polymerization. The initiator solution was fed continuously at 15ml/hour through the end of the reaction period. After a total of 8000 gmonomer mixture was supplied to the reactor, monomer addition wasdiscontinued and the reactor was purged of residual monomer. The totalreaction time was 12 hours. The resulting fluoroelastomer latex wascoagulated by addition of an aqueous calcium nitrate solution, filteredand the fluoroelastomer was washed with deionized water. The polymercrumb was dried for two days at 60° C. The product, composed of 7.7 wt.% ethylene, 42.3 wt. % TFE, 47.0 wt. % PMVE and 3.0 wt. % TFP, was anamorphous fluoroelastomer having a glass transition temperature of −10°C., as determined by differential scanning calorimetry (heating mode,10° C./minute, inflection point of transition). Mooney viscosity, ML-10(121° C.), was 99.

Example 3

[0062] A polymer of the invention (Polymer 3) was prepared by acontinuous emulsion polymerization process, carried out at 90° C. in awell-stirred 4.0-liter stainless steel liquid full reaction vessel. Anaqueous solution, consisting of 1.94 g/hour (g/h) ammonium persulfate,16.0 g/h sodium phosphate dibasic heptahydrate, and 7.0 g/h of ammoniumperfluorooctanoate, was fed to the reactor at a rate of 1.2 L/hour. Thereactor was maintained at a liquid-full level at a pressure of 6.2 MPaby means of a backpressure control valve in the effluent line. After 60minutes, polymerization was initiated by introduction of a gaseousmonomer mixture consisting of 6.3 wt. % ethylene, 36.6 wt. % TFE, 55.9wt. % PMVE and 1.2 wt. % TFP fed through a diaphragm compressor. After4.0 hours, collection of effluent dispersion was begun and continued for20 hours. The effluent polymer dispersion, which had a pH of 6 andcontained 26 wt. % solids, was separated from residual monomers in adegassing vessel at atmospheric pressure. The resulting fluoroelastomerlatex was coagulated by addition of calcium nitrate aqueous solution,filtered and washed with deionized water. The wet crumb was dried in anair oven at approximately 50°-65° C. to a moisture content of less than1 wt. %. About 8 kg of polymer was recovered at an overall conversion of77%. The product, composed of 8.4 wt. % ethylene, 43.2 wt. % TFE, 46.6wt. % PMVE and 1.8 wt. % TFP units, was an amorphous fluoroelastomerhaving a glass transition temperature of −9° C., as determined bydifferential scanning calorimetry (heating mode, 10° C./minute,inflection point of transition). Mooney viscosity, ML-10 (121 °C.), was76.

[0063] Control A

[0064] A control polymer (Control Polymer A) of the prior art was madeby substantially according to the process used to prepare Polymer 1 inExample 1, except that the monomer mixture was comprised of 6 wt. %ethylene, 38 wt. % TFE, 55 wt. % PMVE and 1 wt. %4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB). The resultingfluoroelastomer had a composition of about 8 wt. % E, 44 wt. % PMVE and47 wt. % TFE and 1 wt. % BTFB with a ML-10 (121° C.) of about 50).

Example 4

[0065] A curable composition of the invention (Sample 1) was made bymixing Polymer 1 prepared above with a polyhydroxy curative, acidacceptor, vulcanization accelerator and other ingredients on aconventional two-roll rubber mill, using standard mixing techniquesemployed in the elastomer industry. A comparative curable composition(Comparative Sample A) was made by a similar procedure except that i) afluoroelastomer of the prior art was employed (Control Polymer Aprepared above), which contained BTFB cure site monomer rather than acure site monomer used in the fluoroelastomers of this invention, andii) the comparative composition was crosslinked with a peroxide curingsystem. The formulations are shown in Table I.

[0066] Curing characteristics, tensile properties and compression setresistance were measured according to the Test Methods. ODR measurementswere of slabs at 1770° C.-3° arc, 24 minute motor. Tensiles andcompression set were measured on slabs which had been press cured for 10minutes at 177° C., followed by a postcure of 24 hours at 200° C. inair. The results are also shown in Table I. Cured slabs resulting fromthe bisphenol curable composition of the invention (Sample 1) had muchbetter compression set than slabs resulting from the peroxide curablecomposition of the prior art (Comparative Sample A). TABLE I Ingredient,phr¹ Comp. Sample A Sample 1 Control Polymer A 100 0 Polymer 1 0 100Diak 7² 2.25 0 Luperco ® 101XL³ 2.25 0 TBAHS⁴ 0 2.5 Bisphenol AF 0 2.5Zinc Oxide 6 0 Magnesium Oxide 0 3 Calcium Hydroxide 0 6 MT Carbon Black30 30 Curing Characteristics M_(L), dN · m 27.1 22.3 M_(H), dN · m 74.2108 t_(s)2, minutes 1.2 1.4 tc90, minutes 9.5 8.5 Tensile PropertiesM₁₀₀, MPa 5.0 4.3 T_(B), MPa 9.7 6.9 E_(B), % 235 230 Hardness, Shore A74 76 Compression Set @150° C., 70 hours, % 57 23 @200° C., 70 hours, %63 39

Example 5

[0067] A curable composition of the invention (Sample 2) was made bymixing Polymer 3 prepared above with a polyhydroxy curative, acidacceptor, vulcanization accelerator and other ingredients on aconventional two-roll rubber mill, using standard mixing techniquesemployed in the elastomer industry. A comparative curable composition(Comparative Sample B) was made by the same procedure except that afluoroelastomer of the prior art was employed (Control Polymer Aprepared above), which contained BTFB cure site monomer. Theformulations are shown in Table II.

[0068] Curing characteristics (MDR at 200° C., 24 minutes) were measuredaccording to the Test Methods. The results are also shown in Table II.Sample 2 (a composition of the invention) cured faster than ComparativeSample B (tc90 of 4.32 min. vs. 16.7 min.) and reached a higher state ofcure (M_(H)-M_(L) of 9.07 vs. 1.74). TABLE II Ingredient, phr¹ Comp.Sample B Sample 2 Control Polymer A 100 0 Polymer 3 0 100 TBAHS² 1.961.96 Bisphenol AF 1.5 1.5 Maglite D³ 5.0 5.0 Calcium Hydroxide 3.0 3.0Curing Characteristics M_(L), dN · m 0.70 0.75 M_(H), dN · m 2.44 9.82tc50, minutes 6.0 2.4 tc90, minutes 16.7 4.3

Example 6

[0069] A curable composition of the invention (Sample 3) was made bymixing Polymer 2 prepared above with a polyhydroxy curative, acidacceptor, vulcanization accelerator and other ingredients on aconventional two-roll rubber mill, using standard mixing techniquesemployed in the elastomer industry. A comparative curable composition(Comparative Sample B) was made by a similar procedure except that i) afluoroelastomer of the prior art was employed (Control Polymer Aprepared above), which contained 4-bromo-3,3,4,4-tetrafluorobutene-1(BTFB) cure site monomer rather than a cure site monomer used in thefluoroelastomers of this invention, and ii) the comparative compositionwas crosslinked with a peroxide curing system. The formulations areshown in Table III.

[0070] Curing characteristics, tensile properties and compression setresistance were measured according to the Test Methods. ODR measurementswere of slabs at 177° C.-3° arc, 24 minute motor. Tensiles andcompression set were measured on slabs which had been process cured for10 minutes at 177° C., followed by a postcure of 24 hours at 232° C. inair. The results are also shown in Table III. Cured slabs resulting fromthe bisphenol curable composition of the invention (Sample 1) had muchbetter compression set than slabs resulting from the peroxide curablecomposition of the prior art (Comparative Sample A). TABLE IIIIngredient, phr¹ Comp. Sample B Sample 3 Control Polymer A 100 0 Polymer2 0 100 Diak 7² 2.50 0 Luperco ® 101XL³ 2.50 0 Bisphenol AF Salt⁴ 0 3.15Zinc Oxide 6 0 Magnesium Oxide 0 3 Calcium Hydroxide 0 6 MT Carbon Black30 30 Curing Characteristics M_(L), dN · m 26.2 47.1 M_(H), dN · m 76.7128.8 t_(s)2, minutes 1.3 0.8 tc90, minutes 9.7 3.1 Tensile PropertiesM₁₀₀, MPa 5.6 9.0 T_(B), MPa 15 13 E_(B), % 275 165 Hardness, Shore A 7377 Compression Set @150° C., 70 hours, % 48 34 @200° C., 70 hours, % 5347

What is claimed is:
 1. A specialty fluoroelastomer comprisingcopolymerized units of 10 to 40 mole percent ethylene; 20 to 40 molepercent perfluoro ether selected from the group consisting ofperfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenyl ethers) andperfluoro(alkoxy alkenyl ethers); 32-60 mole percenttetrafluoroethylene; and 0.1 to 15 mole percent of a cure site monomerselected from the group consisting of i) 3,3,3-trifluoropropene-1, ii)trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv)1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene.
 2. Aspecialty fluoroelastomer of claim 1 wherein said copolymerized units ofethylene are present in an amount between 20 and 40 mole percent; saidcopolymerized units of perfluoro ether in an amount between 20 and 30mole percent; said copolymerized units of tetrafluoroethylene in anamount between 40 and 50 mole percent and said copolymerized units ofcure site monomer in an amount between 2 and 10 mole percent.
 3. Aspecialty fluoroelastomer of claim 2 wherein said cure site monomer is3,3,3-trifluoropropene-1.
 4. A specialty fluoroelastomer of claim 2wherein said perfluoro ether is perfluoro(methyl vinyl ether).
 5. Acurable fluoroelastomer composition comprising A) a specialtyfluoroelastomer comprising copolymerized units of 10 to 40 mole percentethylene; 20 to 40 mole percent perfluoro ether selected from the groupconsisting of perfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenylethers) and perfluoro(alkoxy alkenyl ethers); 32-60 mole percenttetrafluoroethylene; and 0.1 to 15 mole percent of a cure site monomerselected from the group consisting of i) 3,3,3-trifluoropropene-1, ii)trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv)1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene; B)0.1 to 10 parts by weight per 100 parts fluoroelastomer of a polyhydroxycuring agent; C) 1 to 20 parts by weight per 100 parts fluoroelastomerof an acid acceptor; and D) 0.1 to 10 parts per 100 partsfluoroelastomer of a vulcanization accelerator.
 6. A curablefluoroelastomer composition of claim 5 wherein said specialtyfluoroelastomer comprises copolymerized units of ethylene present in anamount between 20 and 40 mole percent; said copolymerized units ofperfluoro ether in an amount between 20 and 30 mole percent; saidcopolymerized units of tetrafluoroethylene in an amount between 40 and50 mole percent and said copolymerized units of cure site monomer in anamount between 2 and 10 mole percent.
 7. A curable fluoroelastomercomposition of claim 6 wherein said cure site monomer is3,3,3-trifluoropropene-1.
 8. A curable fluoroelastomer composition ofclaim 5 wherein said perfluoro ether in said specialty fluoroelastomeris perfluoro(methyl vinyl ether).
 9. A curable fluoroelastomercomposition of claim 5 further comprising E) 0.2 to 7 parts by weightper 100 parts fluoroelastomer of an organic peroxide and F) 0.1 to 10parts by weight per 100 parts fluoroelastomer of a multifunctionalcoagent.
 10. A curable fluoroelastomer composition of claim 5 whereinsaid polyhydroxy curing agent B is a curing agent selected from thegroup consisting of i) dihydroxy-, trihydroxy-, andtetrahydroxy-benzenes, -naphthalenes, and -anthracenes; ii) bisphenolsof the formula

where A is a stable divalent radical; x is 0 or 1; and n is 1 or 2; iii)dialkali salts of said bisphenols, iv) quaternary ammonium andphosphonium salts of said bisphenols, v) tertiary sulfonium salts ofsaid bisphenols, and vi) esters of phenols.
 11. A curablefluoroelastomer composition of claim 5 wherein said vulcanizationaccelerator D is chosen from the group consisting of quaternary ammoniumsalts, tertiary sulfonium salts and quaternary phosphonium salts.
 12. Acurable fluoroelastomer composition of claim 11 wherein said cureaccelerator D is selected from the group consisting of i) quaternaryammonium salts of said polyhydroxy crosslinking agent (B), ii)quaternary phosphonium salts of said polyhydroxy crosslinking agent (B)and iii) tertiary sulfonium salts of said polyhydroxy crosslinkingagent.
 13. A curable fluoroelastomer composition comprising A) aspecialty fluoroelastomer comprising copolymerized units of 10 to 40mole percent ethylene; 20 to 40 mole percent perfluoro ether selectedfrom the group consisting of perfluoro(alkyl vinyl ethers),perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenyl ethers);32-60 mole percent tetrafluoroethylene; and 0.1 to 15 mole percent of acure site monomer selected from the group consisting of i)3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii)1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, andv) 2,3,3,3-tetrafluoropropene; B) a compound selected from the groupconsisting of i) quaternary ammonium salts of a bisphenol, ii)quaternary phosphonium salts of a bisphenol and iii) tertiary sulfoniumsalts of a bisphenol; and C) an acid acceptor.
 14. A curablefluoroelastomer composition of claim 13 further comprising E) 0.2 to 7parts by weight per 100 parts fluoroelastomer of an organic peroxide andF) 0.1 to 10 parts by weight per 100 parts fluoroelastomer of amultifunctional coagent.
 15. A curable fluoroelastomer composition ofclaim 13 wherein said quaternary ammonium salt of a bisphenol is a 1:1molar ratio salt of a quaternary ammonium compound and bisphenol AF. 16.A curable fluoroelastomer composition of claim 15 wherein saidquaternary ammonium salt of bisphenol AF is selected from the groupconsisting of a) a tetrapropylammonium/bisphenol AF salt, b) amethyltributylammonium/bisphenol AF salt, and c) atetrabutylammonium/bisphenol AF salt.